SME-08B

Optical Encoder IC

SME-08B Reflective type Optical Encoder IC
Compact package size
3.95mm(L) x 3.4mm(W) x 1.0mm(H)
Two types of products are available for the incremental signal output
Differential analog signal / digital signal
Various built-in functions
Origin detection, LED Auto power control etc

1. SME-08B Overview
The SME-08B is a compact encoder IC that integrates a light source LED and a OEIC (Opto-Electric Integrated Circuit)in a small surface-mount package. The SMD-08B can output a 2-phase differential analog sine wave signal or a 2-phase
digital signal with built-in interpolation function as an incremental signal (A-phase and B-phase) and a digital origin
signal (Z-phase). The incremental signal output is greatly improved by arraying the photodetector to minimize signal
degradation due to mounting misalignment, and is less susceptible to misalignment between the scale and IC.
It is ideal for various applications requiring the following features[Features]Clear molded miniature package 3.95mm (L) × 3.4mm (W) × 1.0mm (H)Selectable output signals in product version
Incremental output: 2-phase analog sine wave signal / 2-phase digital signal
Origin signal width (Digital signal output version only): 90°e / 180°e / 360°e
Analog incremental output
2-phase differential analog sine wave output with signal period of 80μm
High signal-to-noise ratio and excellent Lissajous characteristics can be combined with external interpolation
circuits to achieve higher resolution
Digital incremental output
2-phase digital output with built-in interpolation function
By providing an index pattern within the incremental pattern, the origin signal (Z-phase) is output in a single track
Built-in LED light sourceBuilt-in Automatic Power Control (APC) to compensate for changes in light source brightness due to temperaturechanges and aging
Supply voltage range
Analog output model: 4.5 to 5.5 V
Digital output model: 3.0 to 3.6 V, 4.5 to 5.5 V
Low current consumption 27mA (typ at 5V power supply)Easy positioning/installation
Reflow mount (*confirm suitability of reflow conditions)[Typical Applications]
Encoders for Motion Control
Encoders for motor rotation detection
Encoders for robot and machining center position detection
Consumer devices such as camera lenses that require high-precision position control
Other devices requiring position/speed control, such as printing machines and card readersOther position/speed control applications requiring miniaturization and high accuracy

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2. Principle of operation, features of SME-08B, and product version
The components of the encoder using the SME-08B consist of the LED and OEIC built into the SME-08B and an
external scale. The light emitted from the LED is reflected by the scale, and the bright/dark pattern created by thereflected light on the OEIC is monitored by the photodetector (photodiode) to realize the encoder function.
To monitor the pattern for incremental signals, the OEIC has an array of photodetector with a pitch that is exactly 1/4 ofthe light/dark cycle of the reflected light.
The photo detector array of the pattern for incremental signals is configured to simultaneously monitor several cycles ofreflected light from the scale and output the average value. This photodetector array is designed to provide stable output
even if the SME-08B and the scale deviate slightly from the perfectly parallel state, because the effects of the deviation
are canceled out by the A and B phases.
The photodetectors of the SME-08B have a shape and arrangement suitable for rotary scales. Therefore, in the case of
linear scales or rotary scales with small or large diameters, the output signal amplitude and distortion of thephotodetector may be affected by a mismatch between the light/dark pattern caused by the reflected light from the scale
and the arrangement of the photodetector. As a result, the output signal of the IC may be affected depending on theoperating conditions and environment, such as misalignment between the IC and the scale.
When using a linear scale or a rotary scale with a small or large diameter, please make a thorough evaluation in theactual operating environment.
The SME-08B has two signal output functions: an incremental signal (A-phase and B-phase) and an origin signal(Z-phase). The incremental signal is output as a differential analog signal or a digital signal with built-in interpolation
function. The type of signal output and the width of the origin signal are determined by the product version. The
following four models are available.

Product version

Incremental signal

Interpolation

Z-phase width *1

Power supply

SME-08B20

Analog signal

none

430°e

4.5 to 5.5 V

Digital signal

4x / 8x / 16x(By terminal
setting)

SME-08B21
SME-08B22
SME-08B23

90°e
180°e

3.0 to 3.6 V
4.5 to 5.5V

360°e

*1 Unit of output width (°e): Angular unit of 360 degrees for one cycle of the phase A signal.

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3. Typical SME-08B Encoder Configurations
3.1. Linear Encoder Configuration and Alignment

Scale

SME-08B

A linear encoder can be configured with a linear scale and SME-08B. The optical center of the SME-08B should bealigned with the center of the scale width of the incremental pattern of the linear scale. In addition, the axis of the
package center passing through the optical center and the axis in the longitudinal direction of the scale pattern should beparallel. At this time, make sure that there is no tilt between the scale plane and the SME-08B package surface.

The optical center is located 2.62 mm from the bottom edge of the package on the central axis passing through the
midpoint of the top and bottom edges of the package shown below.

[TOP VIEW]

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3.2. Rotary Encoder Configuration and Alignment

Scale
CW

SME-08B
CCW

A rotary encoder can be configured with a rotary scale and SME-08B. The center of the scale width of the incremental
pattern of the rotary scale should be aligned with the optical center, and the vertical line from the center of rotation of
the scale should be aligned with the center axis of the package passing through the optical center. At this time, makesure that there is no tilt between the plane of the scale and the surface of the SME-08B package.
As shown in the above figure, when the IC placed on the rotation axis side (inside) of the scale is viewed from the back,the rotation direction of the scale is CW (rightward) and CCW (leftward)..

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3.3. Cylindrical Rotary Encoder Configuration

Flexible scale

SME-08B

By using a flexible scale such as PET, it is possible to directly detect the rotation of a cylindrical rotating object, asshown in the drawing above. However, an 80μm pitch scale pattern is required at the joints between the scales to form acomplete scale around the circumference, which must taken into consideration when attaching the scale. Of course, thisis not a problem if the scale is attached to just a portion of the cylinder for detecting rotational position of less than360°.

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Optical Encoder IC

3.4. Scales for SME-08B
As mentioned above, the SME-08B can be combined with a linear or rotary scale to form a linear or rotary encoder.
The scale must be prepared separately from the SME-08B. The following scale manufacturers can provide scales for the
SME-08B, so please contact them for more information.
SME-08B is designed for a scale pattern pitch (period) of 80 µm. The scale pattern should be 80 µm (40 µm forreflective area/40 µm for non-reflective area) to match the specified pitch. If the scale pitch is changed, the signal
output period cannot be changed.

3.4.1. Metal scale
The following manufacturer can provide metal-based scales. Metal scales are said to have excellent corrosion resistanceand durability.
[Metal scale manufacture]
ALPHASEIKO CO.,LTD Sales Department, Encoder Unit315-1 Shimo-ongatamachi, Hachioji-shi, Tokyo, 192-0154, Japan
TEL: +81-42-650-7715
URL: http://www.alphaseiko.jp/
E-mail: info@alphaseiko.jp

3.4.2. Flexible PET scale
The following manufacturer can provide scales using PET as the base material. PET scale is said to be characterized by
its flexibility and thinness.
[Flexible (PET) scale manufacture] Meltec Corporation sales Dept.
1038 Nagareyama, Nagareyama City, Chiba 270-0164, Japan
TEL: +81-4-7178-8800
URL: https://www.e-meltec.jp
E-mail: info@e-meltec.jp

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3.4.3. Pattern of scale
The SME-08B detects refrected light from an incrimental pattern of alternating refrectve and non-refrective areas on thescale and output 2-phase incrimental signal. It is also possible to output an origin signal by placing two types of index
patterns in the incremental pattern, thus eliminating the need for a separate track for origin detection.
See the following section for details on index patterns for rotary and linear scales.

3.4.3.1. Rotary scale
The rotary scale of SME-08B should have the following dimensions at thecenter of the scale pattern width (ROP).
Reflective pattern width (Ww): 40 μm
Non-reflective area pattern width (Wb): 40 μm
Pitch of the pattern (Pb): 80 μm
Index pattern1: 200 μm
Index pattern2: 120 μm
Six non-reflective patterns and five reflective patterns should be placed
between the index patterns. The SME-08B should be placed on the inside of
the scale (lower part of the figure, on the side of the scale rotation axis), in
which case the position indicated by ▼ in the figure is the logical origin.
If the number of patterns required for the scale (PPR: number of reflection andnon-reflection pairs) is fixed, the radius of the center of the scale pattern (Rop)can be obtained from the following formula.
Rop (mm) = ( PPR × 0.08 ) ÷ π ÷ 2
For example, if the number of patterns is 865, then 865 × 0.08 ÷ π ÷ 2 = 11.0135, resulting in 11.0135 mm as theradius of the center of the pattern.

3.4.3.2. Linear scale
For the linear scale pattern of SME-08B, each pattern part should have a fixed width and be arranged as shown in the
figure below. In the case of the arrangement shown below, SME-08B is placed at the lower position in the figure, andthe origin position in the figure is the logical origin.
If there is no index pattern on the linear scale, SME-08B can be placed in either bellow or above in the figure bellow.

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4. Reference Information about SME-08B Specifications
4.1. Reference Information about Package
4.1.1. Layout of SME-08B Internal Components
The LED and OEIC are arranged as shown below.
[TOP VIEW]

SME-08B20

SME-08B21, B22, B23

4.1.2. Environmental Data
The SME-08B is a lead-free, PVC-free (polyvinyl chloride), Halogen-free, and RoHS compliant product.

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4.2. Electrical Specifications Reference Information
4.2.1. Basic Connection
The SME-08B should be used with bypass capacitors as shown below. The 0.1 µF capacitor should be placed as close
to the SME-08B as possible. Ceramic capacitors with good frequency response are suitable as bypass capacitors.
[Typical Connection]

SME-08B20

SME-08B21, B22, B23

4.2.2. Differential Analog Output (SME08B20)
The analog output type SME-08B20 output 80 µm period sine wave signals CHA and CHB with phase difference of 90
degrees, and their inverted signals CHAB and CHBB. The differential type outputs, which pair the forward and inverted
signals of phase A and B, respectively, provide countermeasures against common noise generated by external electricfields.
An example of differential output wireing is shown in the figure bellow.

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Optical Encoder IC

Each of the four analog signals has an offset relative to VDD/2, the reference voltage. If necessary, offset correction
should be performed be an external circuit.

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Optical Encoder IC

4.2.3. Interpolation setting and Z-phase output
The analog incremental and origin signals for SME-08B20 and the interpolated digital incrimental and origin signals of
SME-08B21, B22 and B23 for each interpolation setting are shown in the timing diagram below.

4.2.3.1. Analog output (SME-08B20)[Direction: CCW]

[Direction: CW]

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Optical Encoder IC

4.2.3.2. Digital output (SME-08B21, B22, B23)
[Direction: CCW]

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SME-08B

Optical Encoder IC[Direction: CW]

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5. Handling Precautions
Ensure the gray portion containing the LED and OEIC, shown in the
figure on the right, clean and free from dust and other contaminants.
If it is dirty, gently wipe the surface with a soft clean cloth dipped in methanol or
ethanol to remove all contaminants. The use of other liquids or wiping vigorously
may cause scratching, clouding, or otherwise damage the surface of the encoder.
Exercise caution when cleaning the device surface.
Avoid direct contact with the SME-08B and scale when handling, installing, or
adjusting.
Ensure that the operating temperature of any unit or housing containing the
SME-08B will not exceed the temperature specifications of the device.
Please note that there is the potential that strong localized light sources may
affect the encoder output.
The light intensity of the SME-08B built-in LED does not exceed the value forClass 1 standard visible LED eye safety as prescribed by IEC60825-1.

6. USAGE AND PRECAUTIONSThis product is designed and manufactured to the generally accepted standards of reliability as expected for use ingeneral electronic and electrical equipment, such as personal equipment, machine tools, and measurement
equipment. This product is not designed and manufactured to be used in any other special equipment requiringextremely high level of reliability and safety, such as aerospace equipment, nuclear power control equipment, medical
equipment, transportation equipment, disaster prevention equipment, security equipment.
If you wish to use this product in equipment requiring extremely high level of reliability, please contact our sales
department or representative in advance.
In the event that this product is used in such equipment, please take scrupulous care and apply fail-safe techniques
including redundancy and malfunction prevention in order to prevent damage to life, health, property, or infrastructureetc. in case there is some malfunction in the product.

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SME-08B

Optical Encoder ICThis Application Note is provided as a reference for product introduction and customer evaluation purposes for thisproduct. Typical characteristics and other values mentioned in this document are provided as reference data only todemonstrate principles and trends; this document does not include manufacturing tolerances and other characteristics
data. Devices should only be used after thorough evaluation under actual operating conditions.

Please pay your attention to the following points at time of using the products shown in this document.
1. The products shown in this document (hereinafter ”Products”) are designed and manufactured to the generally
accepted standards of reliability as expected for use in general electronic and electrical equipment, such as
personal equipment, machine tools and measurement equipment. The Products are not designed and manufactured
to be used in any other special equipment requiring extremely high level of reliability and safety, such as aerospaceequipment, nuclear power control equipment, medical equipment, transportation equipment, disaster prevention
equipment, security equipment. The Products are not designed and manufactured to be used for the apparatus thatexerts harmful influence on the human lives due to the defects, failure or malfunction of the Products.
If you wish to use the Products in that apparatus, please contact our sales section in advance.
In the event that the Products are used in such apparatus without our prior approval, we assume no responsibility
whatsoever for any damages resulting from the use of that apparatus.
2. NPC reserves the right to change the specifications of the Products in order to improve the characteristics orreliability thereof.
3. The information described in this document is presented only as a guide for using the Products. No responsibility is
assumed by us for any infringements of patents or other rights of the third parties which may result from its use. No
license is granted by implication or otherwise under any patents or other rights of the third parties. Then, we assume
no responsibility whatsoever for any damages resulting from that infringements.
4. The constant of each circuit shown in this document is described as an example, and it is not guaranteed about its
value of the mass production products.
5. In the case of that the Products in this document falls under the foreign exchange and foreign trade control law orother applicable laws and regulations, approval of the export to be based on those laws and regulations are necessary.
Customers are requested appropriately take steps to obtain required permissions or approvals from appropriate
government agencies.
6. When exporting customer’s products that use the Products, customers must comply with the "Foreign Exchange andForeign Trade Act" and other export-related laws and regulations, and follow the necessary procedures inaccordance with those laws and regulations. Do not use the Products in equipment whose sale is prohibited byexport-related laws and regulations ("JP Foreign Exchange and Foreign Trade Act" and "US Export Administration
Regulations", etc.). In addition, please do not sell the Products to users who are expected to use it for the above
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SEIKO NPC CORPORATION
2-9-4, Taito, Taito-ku,
Tokyo 110-0016, Japan
Telephone: +81-3-6747-5300
Facsimile: +81-3-6747-5303
https://www.npc.co.jp/
Email:sales@npc.co.jp

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